1. Field of the Invention
This invention relates to the field of solid phase binding assays using ligands and their specific binding receptors. In particular, it relates to the use of such assays to detect in a quantitative or semi-quantitative manner the amount of an analyte in a sample suspected of containing the analyte.
The ability to employ naturally occurring receptors or antibodies directed against specific compounds in assaying for the presence of a compound of interest has created a burgeoning immunoassay business. In these assays, a homologous pair of specific binding pair members (“sbp members”), usually an immunological pair, comprising a ligand and a receptor (antiligand) is involved, wherein one of the sbp members is labelled with a label which provides a detectable signal. The immunoassay methodology results in a distribution of the signal label between signal label bound in a complex of the sbp members and unbound signal label. The differentiation between bound and unbound signal label can be a result of physical separation of bound from unbound signal label or modulation of the detectable signal between bound and unbound signal label.
For the most part, immunoassays that have been directed towards quantitative determinations have required complex instrumentation, relatively sophisticated equipment, careful experimental technique and skilled operators, such as is found in clinical laboratories. Therefore, quantitative and semi-quantitative immunoassays have found less extensive application in settings such as the home, a medical practitioner's office, a health care maintenance organization setting or a primary care setting in a hospital where complex instrumentation is unavailable and testing is typically done by untrained personnel. Even in a clinical laboratory, simple and rapid tests for screening diagnostic, monitoring or prognosis for outcome purposes done by inexperienced personnel could provide substantial economies in terms of timeliness of results and labor costs.
In developing an immunoassay, there are many considerations. One consideration is to provide substantial differentiation between the observed signal resulting from signal label when bound as compared to unbound. Another consideration is to minimize interference from endogenous materials in the sample suspected of containing the compound of interest. A further consideration is the ease with which the observed signal can be detected and serve to differentiate between concentrations in the concentration range of interest. Other factors include the ease of preparation of reagents, the precision with which the samples and reagents must be prepared and measured, the storage stability of the reagents, the number of steps required in the protocol, and the proficiency with which each of the steps must be performed. Therefore, in developing a quantitative assay that can be used by untrained personnel, such as assays to be performed in the home, medical offices and the like, the observed result should be minimally affected by variations in the manner in which the protocol is carried out and the techniques for performing the various steps should be simple. Preferably, one-step protocols should be employed.
Recently, a variety of solid phase binding assays which do not require complex instrumentation have been described for detection of analyte in a sample suspected of containing the analyte. However, such assays typically provide qualitative results. Frequently, such solid phase assays also employ a multiplicity of steps, such as wash steps, to separate unbound label from bound label. Therefore, it would be desirable to provide simple, one-step solid phase non-instrumented methods and devices for quantitating an analyte in a sample suspected of containing the analyte. This invention fulfills that and other needs.
2. Summary of Related Art
A Noninstrumented Quantitative Test System and Its Application for Determining Cholesterol Concentration in Whole Blood; M. P. Allen et al.; Clinical Chemistry, Vol 36 No. 9: 1591–1597 (1990); discloses a noninstrumental solid phase method of quantitating cholesterol using enzymatic conversion of immobilized substrate.
One-Step Competitive Immunochromatographic Assay for Semiquantitative Determination of Lipoprotein(a) in Plasma; S. C. Lou et al.; Clinical Chemistry, Vol. 36 No. 4: 619–624 (1993); discloses semiquantitative measurement of lipoproteins using a solid phase assay with multiple capture bars.
Immunochemical semi-quantitative Assay Method—and appts.; Patent No. WO 94/28415A to H. Manita; discloses a semiquantitative chromatographic immunochemical assay method which consists of passing the sample for assay through a predetermined amount of an immobilized antibody (IAb) which recognizes the substance to be assayed, then allowing the excess to pass to a label (such as a color indicator) which indicates its presence.
Concentrating Immunochemical Test Strip; European Patent No. EP 0 191 640 A2 to D. Calderhead et al. (1986); discloses solid phase methods and devices for detecting analytes involving contacting a test strip containing a first sbp member with a test solution comprising the analyte and a second sbp member complementary to the analyte. The first sbp member is capable of binding the second sbp member.
U.S. Pat. No. 4,861,711; H. Friesen et al. (1989); discloses a solid-phase diagnostic device for the determination of biological substances.
U.S. Pat. No. 4,740,468; L. Weng et al. (1988); discloses a solid phase specific binding method and device for detecting an analyte.
U.S. Pat. No. 4,806,311; A. Greenquist (1989); discloses a multi-zone test device for analyte determination using a labelled reagent and immobilized reagent which are specific binding partners whose binding to each other depends on the amount of analyte present and a detection zone with an immobilized binding substance for the labelled reagent.
U.S. Pat. No. 4,168,146; A. Grubb et al. (1979); discloses a solid phase method and strip with bound antibodies.
U.S. Pat. No. 4,959,307; J. Olson (1990); discloses a solid phase method and device for detecting an analyte involving contacting a test solution containing sample, antibody to the analyte and a labelled analyte with a test strip containing an immobilized first receptor that binds to the labelled analyte and an immobilized second receptor that binds to the antibody.
U.S. Pat. No. 4,435,504; R. Zuk (1984); discloses a chromatographic immunoassay employing a sbp member and a label conjugate.
U.S. Pat. No. 4,883,688; T. Houts et al. (1989) discloses an immunochromatographic device which quantitates analyte as a function of the distance migrated by a sbp member along the device.